The development of modular high capacity telephone switching equipment has given telephone companies the opportunity of providing a standard type of switching system to customers even though they may have different needs and telephone traffic demands on their system. The modularity of these systems allows the customers to increase their traffic handling capacity without having to exchange their equipment with systems having increased capacity. For example, a customer can obtain such a switching system with a minimum number of interface boards and circuit packs to meet its immediate demand. However, if the customer requires increased capacity from the system, additional interface boards and circuit packs can be obtained and integrated with the original system at minimal cost to the customer.
However, it was found that edge critical signals such as the clock and frame pulse signals on the backplane assembly were affected by the characteristic impedance discontinuities that exist between the loaded and unloaded portions of the backplane. For example, it was found that the impedance along the backplane connecting lines dropped considerably from an unloaded to a loaded backplane section. This resulted in the degradation of the clock and frame pulse signals. This degradation increased the number of errors and faults in the system.
It is therefore an object of the present invention to reduce the characteristic impedance discontinuities that exist between the loaded and unloaded portions of the backplane by the addition of dummy loads on unused backplane termination slots.
According to a first aspect of the present invention, there is provided a bus interface loading assembly used to equalize the electrical loads of termination slots on a backplane assembly, comprising: loading means adapted to be connected on said backplane at unused slots theroef and adapted to emulate a real load such that the characteristic impedance discontinuities of the backplane assembly are minimized.
According to a second aspect of the present invention, there is provided a bus interface loading assembly used to equalize the electrical loads of termination slots on the backplane assemblies bussed lines of edge critical signals of telephone switching systems, comprising: loading means adapted to be connected on said backplane at unused slots thereof and adapted to emulate a real load such that the characteristic impedance discontinuities of the backplane assembly are minimized.